1. Field of the Invention
The present invention relates to a bearing structure of a wiper arm attached to an automobile or the like.
2. Description of the Related Art
In this kind of wiper arm, an arm shank with a blade at its leading end is rockably pivoted at the leading end of an arm support whose base end is integrally fixed to a wiper shaft, and the arm shank and the arm support are urged by a spring beyond a supporting point so that the blade abuts against a glass plane with a proper wiping force.
Conventionally, as shown in FIG. 6, when an arm shank is rockably pivoted at an arm support 2, a bushing unit 6, which is formed by insert-molding a bearing formed by sintering into a resin material, is pressed into a bearing portion of the arm support so as to prevent the arm support 2 and the bearing from being directly in contact with each other. Although the arm support 2 is coated beforehand, a coating material intrudes into a bearing hole 2a of the arm support 2. This makes it difficult to control the inner diameter of the bearing hole 2a.
On the other hand, since the outer surface of the bearing is smoothed in a sizing process when the bearing is manufactured, the adhesive force of the bearing to the resin material is small. Therefore, when the bushing unit 6 is pressed into the bearing hole 2a of the arm support 2 by pushing the back end of the bushing unit 6, the press-in load is applied to the resin material at the leading end of the bushing unit 6. If the press-in load is heavy, the resin material sometimes separates from the bearing and cracks "A" are generated due to differences in the inner diameter of the bearing hole 2a resulting from the intrusion of the coating material. This is a factor in lowering the reliability of the wiper arm.